1. Field of the Invention
The present invention relates generally to a control device which controls switching elements of an electric power inverter circuit having connecting points, being connected with respective terminals of an electric rotating machine and being set at respective electric potentials different from one another, by changing an on (i.e., conductive) or off (i.e., non-conductive) state of selected switching elements to the off or on state and which controls a controlled variable of the electric rotating machine connected with the connecting points of the electric power inverter circuit.
The present invention relates more particularly to the control device which has a predicting unit that performs a prediction for the controlled variable of the electric rotating machine, on the assumption that the electric power inverter circuit is set in one of operating states to set the switching elements instates corresponding to the operating state, an operating state determining unit that determines one of the operating states of the electric power inverter circuit by using the predicted controlled variable and an instructed value of the controlled variable, and a control unit that controls the electric power inverter circuit to actually set the electric power inverter circuit in the determined operating state.
2. Description of Related Art
A control method for a three-phase motor receiving driving power through an inverter has been used. In this method, an operating state of the inverter is repeatedly switched or changed to another state to adjust an alternating current supplied to the motor and to control the motor. For example, a model predict ion control using a motor driving system has been proposed in Published Japanese Patent First Publication No. 2008-228419.
In this model prediction control, an alternating current flowing through a three-phase motor is predicted each time an inverter is set in one of various operating states, and the inverter is controlled to be set in an appropriate operating state in which a difference between the predicted current and an instructed current can be minimized. The value of the predicted current is predicted by using a detected value of an alternating current actually flowing through the motor as an initial value. In the model prediction control, the inverter is controlled so as to optimize a change in the current predicted based on an output voltage of the inverter. Therefore, in a transition period of time until the value of the instructed current becomes constant, the current outputted from the inverter can preferably follow the instructed current. Accordingly, the model prediction control can be useful for a control device of a motor generator requiring a high follow-up performance in a transition period as an on-board primary component.
When the operating state of the inverter is switched to another one every changing period, it is well known that ringing occurs generally in the current actually flowing through the three-phase motor. When the value of the current detected during a ringing occurring period is used to predict the current flowing through the motor, controllability for the motor is sometimes lowered. To prevent the controllability from being lowered, a control method using a motor driving device is proposed in Published Japanese Patent First Publication No. 2010-74902. In this control method, an alternating current flowing through a three-phase motor is detected when ringing generated in the current disappears.
However, in the model prediction control, a predicting period is required to perform the calculation for predicting the alternating current of the motor, and the precision in the control performed for the motor can be heightened when the changing period of the operating state is shortened. Therefore, when the detection of an alternating current flowing through the motor is stopped until ringing generated in the current disappears, it is difficult to perform the model prediction control at a high controllability for a three-phase motor.